U.S. patent application number 12/345960 was filed with the patent office on 2009-07-30 for method and apparatus for structuring a radiation-sensitive material.
This patent application is currently assigned to Carl Zeiss SMT AG. Invention is credited to Heiko Feldmann.
Application Number | 20090191490 12/345960 |
Document ID | / |
Family ID | 40638055 |
Filed Date | 2009-07-30 |
United States Patent
Application |
20090191490 |
Kind Code |
A1 |
Feldmann; Heiko |
July 30, 2009 |
METHOD AND APPARATUS FOR STRUCTURING A RADIATION-SENSITIVE
MATERIAL
Abstract
A method and to an apparatus for structuring a
radiation-sensitive material are disclosed. The method can include
using a dynamic mask to generate a first radiation pattern in a
layer of the radiation-sensitive material, where the first
radiation pattern has a thickness that is at most 50% of the
thickness of the layer of the radiation-sensitive material. The
method can also include using the dynamic mask to generate a second
radiation pattern in the layer of the radiation-sensitive material.
The dynamic mask can be configured to change its structure
dynamically, and the first radiation pattern can be different from
the second radiation pattern.
Inventors: |
Feldmann; Heiko; (Aalen,
DE) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
Carl Zeiss SMT AG
Oberkochen
DE
|
Family ID: |
40638055 |
Appl. No.: |
12/345960 |
Filed: |
December 30, 2008 |
Current U.S.
Class: |
430/322 ;
355/67 |
Current CPC
Class: |
G02B 26/085 20130101;
G03F 7/70416 20130101; G03F 7/70291 20130101; G03F 7/70341
20130101 |
Class at
Publication: |
430/322 ;
355/67 |
International
Class: |
G03F 7/20 20060101
G03F007/20; G03B 27/54 20060101 G03B027/54 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 2008 |
DE |
10 2008 006 438.6 |
Claims
1. A method, comprising: using a dynamic mask to generate a first
radiation pattern in a layer of the radiation-sensitive material,
the first radiation pattern having a thickness that is at most 50%
of a thickness of the layer of the radiation-sensitive material;
and using the dynamic mask to generate a second radiation pattern
in the layer of the radiation-sensitive material, wherein the
dynamic mask is configured to change its structure dynamically, and
the first radiation pattern is different from the second radiation
pattern.
2. The method according to claim 1, wherein the dynamic mask is a
micromirror array.
3. The method according to claim 1, wherein the method comprises
using projection optics with a numerical aperture of at least
0.9.
4. The method according to claim 1, wherein the first radiation
pattern is focused in a first plane in the layer of
radiation-sensitive material, the second radiation pattern is
focused in a second plane in the layer of radiation-sensitive
material, and the first plane is different from the second
plane.
5. The method according to claim 1, wherein a thickness of the
second radiation pattern is at most 50% of the thickness of the
layer of radiation-sensitive material.
6. The method according to claim 1, further comprising: using
projection optics to project an illumination distribution generated
by the dynamic mask onto the layer of the radiation-sensitive
material to generate the first and second radiation patterns; and
obliquely moving the layer of radiation-sensitive material to a
focus plane of the projection optics.
7. The method according to claim 6, wherein the layer of the
radiation-sensitive material is tilted relative to the focus plane
of the projection optics.
8. The method according to claim 1, further comprising: after
generating the first radiation pattern, moving the layer of the
radiation-sensitive material in a thickness direction of the layer
of the radiation-sensitive material; and subsequently generating
the second radiation pattern.
9. The method according to claim 8, further comprising: after
generating the second radiation pattern, moving the layer of the
radiation-sensitive material in a direction lateral to the
thickness direction of the layer of the radiation-sensitive
material; and subsequently generating third and fourth radiation
patterns in the layer of the radiation-sensitive material, the
third and further radiation patterns being in different planes of
the layer of the radiation-sensitive material.
10. The method according to claim 1, wherein: the first and second
radiation patterns are generated by a respective illumination
distribution produced by the dynamic mask being projected onto the
layer of the radiation-sensitive material via projection optics;
and an aberration of the projection optics is changed between the
projections of the first and second radiation patterns.
11. The method according to claim 1, wherein an immersion fluid is
disposed on the radiation-sensitive material, the refraction index
of the immersion fluid corresponding to the refraction index of the
radiation-sensitive material.
12. The method according to claim 1, wherein the
radiation-sensitive material is a nonlinear resist.
13. The method according to claim 1, wherein a plate of varying
thickness made of translucent material is disposed above the
radiation-sensitive material, and an intermediate space between the
radiation-sensitive material and the plate is filled with an
immersion fluid.
14. The method according to claim 13, wherein the plate is
wedge-shaped in form, and the respective section of the
radiation-sensitive material between a focus plane of the
projection optics and the surface of the radiation-sensitive
material facing towards the plate is also wedge-shaped in form, the
wedge formed by the plate and the wedge formed in the
radiation-sensitive material having opposing orientations.
15. The method according to claim 14, wherein the immersion fluid
disposed between the plate and the radiation-sensitive material
also fills a wedge-shaped volume, the wedge formed by the immersion
fluid having the same orientation as the wedge formed by the
respective section of the radiation-sensitive material.
16. The method according to claim 14, wherein the surface of the
plate facing away from the immersion fluid and the focus plane of
the projection optics are parallel to one another.
17. The method according to claim 1, further comprising using a
single development step to develop at the same time latent images
generated by the first and second radiation patterns in the layer
of the radiation-sensitive material.
18. The method according to claim 1, wherein the layer of the
radiation-sensitive material has a thickness of less than 1 mm.
19. The method according to claim 1, wherein a ratio between the
thickness of the layer of the radiation-sensitive material and an
area of the layer of the radiation-sensitive material is less than
0.01 m.sup.-1.
20. The method according to claim 1, wherein the layer of the
radiation-sensitive material is on a wafer configured to be used in
semiconductor manufacturing.
21. The method according to claim 1, wherein a characteristic
property of the layer of the radiation-sensitive material changes
when irradiated with a radiation intensity exceeding a threshold
intensity.
22. A method, comprising: using a micromirror array to generate a
first radiation pattern in a layer of the radiation-sensitive
material, the first radiation pattern having a thickness that is at
most 50% of a thickness of the layer of the radiation-sensitive
material; and using the micromirror array to generate a second
radiation pattern in the layer of the radiation-sensitive material,
wherein the first radiation pattern is different from the second
radiation pattern.
23. A system, comprising: an apparatus configured to form images in
a layer of a radiation-sensitive material, the apparatus comprising
a dynamic mask configured to change its structure dynamically.
24. The system of claim 23, wherein the dynamic mask is micromirror
array.
25. The system of claim 24, further comprising a device to control
respective positions of micromirrors in the micromirror array.
26. The system of claim 24, wherein: the micromirror array
comprises a plurality of micromirrors; in a first arrangement of
the plurality of micromirrors, the apparatus is capable of forming
a first radiation pattern in the layer of the radiation-sensitive
material; in a second arrangement of the plurality of micromirrors,
the apparatus is capable of forming a second radiation pattern in
the layer of the radiation-sensitive material; and the first
radiation pattern is different from the second radiation
pattern.
27. The system of claim 26, further comprising projection optics
configured to project an illumination distribution generated by the
dynamic mask onto the layer of the radiation-sensitive material to
generate the first and second radiation patterns.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims benefit under 35 U.S.C. .sctn. 119
of German patent application DE 10 2008 006 438.6, filed Jan. 28,
2008, the entire contents of which are hereby incorporated by
reference.
FIELD
[0002] The disclosure relates to a method and to an apparatus for
structuring a radiation-sensitive material.
BACKGROUND
[0003] Photon crystals, interconnection layers of semiconductor
components and micromechanical elements can involve
three-dimensional structuring of elements in the field of
microelectronics. Often, generating three-dimensional structures
involves lithographic methods in which semiconductor elements are
generated layer by layer using different masks. Such methods can
involve applying a photoresist, also called resist, to a carrier
and exposing the photoresist using a first lithographic mask. This
can be followed by a chemical development step in which the
illumination pattern in the photoresist generated during the
preceding exposure is translated into a physical structure in the
photoresist. Here either exposed regions are removed from the
photoresist or, conversely, exposed regions remain while the
unexposed regions surrounding the latter are removed from the
photoresist. The result is a two-dimensionally structured
photoresist layer. A three-dimensional structure can be achieved by
appropriately repeating these steps a number of times with
different lithography masks.
SUMMARY
[0004] In some embodiments, the disclosure provides a method and/or
an apparatus configured so that three-dimensional structuring of a
radiation-sensitive material can be achieved in a relatively
time-efficient and/or inexpensive manner.
[0005] In certain embodiments, the disclosure provides a method of
structuring a radiation-sensitive material. The method can include
providing a layer of the radiation-sensitive material, which is
configured such that, when irradiated with a radiation intensity
exceeding a threshold intensity, a characteristic property of the
radiation-sensitive material is changed. The method can also
include providing a dynamic mask which is configured to change its
structure dynamically, and generating via the dynamic mask a first
radiation pattern in the radiation-sensitive material layer such
that the extension of the first radiation pattern, in which the
radiation intensity exceeds the threshold intensity, is at most 50%
of the thickness of the material layer in the thickness direction
of the material layer at the individual points of the material
layer. In addition, the method can include generating via the
dynamic mask a second radiation pattern in the radiation-sensitive
material layer.
[0006] In some embodiments, the disclosure provides an apparatus
for structuring a radiation-sensitive material. The apparatus can
include a holding device for holding a layer of the
radiation-sensitive material which is configured such that, upon
irradiation with a radiation intensity exceeding a threshold
intensity, a characteristic property of the radiation-sensitive
material is changed. The apparatus can also include a dynamic mask
which is configured to change its structure dynamically. The
apparatus can further include a control device which is configured
to control the apparatus such that a first radiation pattern is
generated via the dynamic mask in the radiation-sensitive material
layer. The extension of the first radiation pattern, in which the
radiation intensity exceeds the threshold intensity, is at most 50%
of the thickness of the material layer in the thickness direction
of the material layer at the individual points of the material
layer. A second radiation pattern can also be generated via the
dynamic mask in the radiation-sensitive material layer.
[0007] The radiation-sensitive material can, for example, be a
so-called resist or photoresist (e.g., having a layer thickness of
10 .mu.m). Upon irradiation with electromagnetic radiation, for
example of a specific wavelength range, the radiation-sensitive
material changes a characteristic property when the radiation
exceeds a specific radiation intensity. In some embodiments, the
change in the characteristic property can be that the
radiation-sensitive material is changed upon exposure such that the
radiation-sensitive material becomes chemically soluble so that in
a subsequent chemical development step, contrary to the non-exposed
material, the exposed portion of the radiation-sensitive material
is removed. An example of this is positive resist. Conversely, in
certain embodiments, the radiation-sensitive material can be
configured (e.g., like a negative resist) so that the portion of
the radiation-sensitive material that is not sufficiently exposed
is removed in the development step.
[0008] In some embodiments, a first radiation pattern is generated
in the radiation-sensitive material layer via a dynamic mask. The
first radiation pattern can be substantially a radiation
distribution extending two-dimensionally within the material layer,
and can also extend in the thickness direction of the material
layer. In certain embodiments, the extension of the radiation
pattern in the thickness direction of the material layer is at most
50% of the thickness of the material layer at the individual points
of the material layer (at respective surface points of the material
layer in the perpendicular projection to the material layer). Here
the extension of the radiation pattern is understood as meaning the
extension in which the radiation intensity exceeds the threshold
intensity of the radiation-sensitive material.
[0009] In certain embodiments, the radiation pattern has a depth of
focus of at most 50% of the radiation-sensitive material. The mask
with which the first radiation pattern is produced can be
configured as a so-called "dynamic mask". Since this is not a
conventional (static) mask, the structuring method can also be
called a mask-free method. The dynamic mask is designed to change
its structure dynamically, and can for example be designed as a
micromirror array, which is sometimes called a DMD (Digital
Micromirror Device).
[0010] By using a dynamic mask, a number of radiation patterns can
be generated one after the other in the radiation-sensitive
material without changing the mask. Therefore, the individual
radiation patterns can be generated in rapid temporal succession.
Furthermore, the method may not involve, for example, readjusting
an additional mask so that the alignment of the individual
radiation patterns in relation to one another can also be
implemented with a high degree of precision. Because the extension
of the first radiation pattern, in which the radiation intensity
exceeds the threshold intensity, is at most 50% of the thickness of
the layer in the thickness direction of the material layer at the
individual points, it is possible to expose only a specific
vertical partial region of the radiation-sensitive material or a
partial layer of the radiation-sensitive material with the first
radiation pattern.
[0011] By generating a second radiation pattern, another vertical
region of the radiation-sensitive layer can be exposed. It is
therefore possible to expose the radiation-sensitive layer plane by
plane with the result being a three-dimensional structuring of the
radiation-sensitive material. This means that by exposing different
depth layers in the radiation-sensitive material layer with
different radiation distributions, it becomes possible to provide
the radiation-sensitive layer with a desired structure not just in
the two dimensions of its main extension, but also in the direction
of its thickness extension. In other words, the radiation-sensitive
layer can be divided virtually into a number of slices lying on top
of one another which are respectively provided separately with
their own two-dimensional structuring.
[0012] In certain embodiments, the dynamic mask is in the form of a
micromirror array. As already mentioned above, this type of
micromirror array is sometimes called a DMD (Digital Micromirror
Device). This type of micromirror array can, for example, include
10,000.times.10,000 mirrors which respectively have an area of
8.times.8 .mu.m. The mirrors can be controlled individually. The
micromirrors are for example mounted on special pivot pins and are
tilted by electrostatic fields. The electrostatic fields are
generated, for example, by switch logics located behind the
micromirrors. By tilting a micromirror the beam reflected by this
mirror can be deflected so that it no longer passes through
downstream projection optics. In this way, by controlling the
micromirror, the illumination of a pixel illuminated by this
micromirror can be switched on or off. Using an array of
10,000.times.10,000 micromirrors, a pixel pattern of
10,000.times.10,000 pixels can be flexibly reconfigured (the pixel
pattern can, for example, be reconfigured from the first radiation
pattern into the second radiation pattern). In some embodiments,
the mirrors can be reduced by a ratio of 1:267 when imaging onto
the radiation-sensitive medium. This can produce a pixel size of 30
nm in the focus plane and a field size of 300 .mu.m.times.300
.mu.m. The vertical resolution or resolution in the thickness
direction of the material layer can be estimated from a Strehl
ratio of 80%, and this corresponds to a RMS wavefront deviation of
0.071.lamda.. In a horizontal direction the resolution can be
estimated as 0.5.times..lamda./NA. .lamda. is the wavelength of the
light used for irradiating the radiation-sensitive material and NA
the numerical aperture of projection optics used. Horizontal
resolutions of for example 80 nm can therefore be achieved. Smaller
dot sizes can be achieved by using non-linear resists, special
illumination settings and by using resolution-enhancing methods,
such as, for example, phase masks and off-center illumination.
[0013] In some embodiments, the radiation patterns are projected
via projection optics with a numerical aperture of at least 0.9
(e.g., at least 1.2). With this type of high numerical aperture, a
relatively small depth of focus can be achieved in the material
layer. This can enable structuring of the radiation-sensitive
material with high resolution in the thickness direction of the
material layer.
[0014] In certain embodiments, the first radiation pattern in a
region of the material layer is focused onto a first focus plane in
relation to the material layer, and the second radiation pattern in
the same region is focused onto a second focus plane in relation to
the material layer. The second focus plane is advantageously offset
in relation from the first focus plane in the thickness direction
of the material layer. In other words, the first radiation pattern
is focused onto a first focus position in relation to the material
layer, and the second radiation pattern is focused onto a second
focus position in relation to the material layer.
[0015] In certain embodiments, the extension of the second
radiation pattern, in which the radiation intensity exceeds the
threshold intensity, is at most 50% of the thickness of the
material layer in the thickness direction of the material layer at
the individual points of the material layer. This can enable
independent structuring of individual layers within the material
layer by the individual radiation patterns.
[0016] In some embodiments, the radiation patterns are respectively
generated by an illumination distribution generated by the dynamic
mask being projected via projection optics onto the material layer,
and by obliquely moving the material layer to the focus plane of
the projection optics. Here the rotational position of the material
layer can basically be adjusted differently in relation to the
focus plane. For example, the material layer can be aligned
parallel to the focus plane or also have other rotational positions
while it is moved obliquely to the focus plane. Using the oblique
movement of the material layer, a region to be exposed can be
disposed in temporal succession at different focus positions. If
the structure of the mask is now changed dynamically and exposed at
appropriate times onto the material layer, a number of radiation
patterns can be generated in an efficient and time-saving way at
different positions within the thickness extension of the material
layer. In certain embodiments, the angle between the movement
direction and the focus plane is 1.9.degree..
[0017] In some embodiments, the material layer is moved along a
plane tilted in relation to the focus plane of the projection
optics, and is thus aligned parallel to the tilted plane. This
means that the material layer is moved in the plane in which it is
disposed. The possibility is therefore offered of exposing points
in different depth positions in relation to the material layer at
the given time with an individual radiation pattern. This can
enable particularly efficient three-dimensional structuring of the
material layer because parallel structuring is thus made possible.
At a given time, regions already previously exposed in a first
depth layer can be structured in a second depth layer lying over
the latter, whereas regions which are disposed in the second depth
layer in the course of the moving or the scanning movement of the
material layer at a later time can be structured in the first depth
layer at the same time. In certain embodiments, the tilt angle
between the material layer and the focus plane is 1.9.degree..
[0018] In some embodiments, after generation of the first radiation
pattern, the material layer is moved in the thickness direction of
the material layer, and the second radiation pattern is then
generated. In particular, the radiation patterns can be generated
by the respective illumination distribution generated by the
dynamic mask projected onto the material layer via projection
optics. After generation of the first radiation pattern, the
material layer can be moved along the optical axis of the
projection optics, and the second radiation pattern can then be
generated. With this method the material layer can also be
structured three-dimensionally in a very efficient way. Therefore,
a thickness section of the material layer can be exposed with the
first radiation pattern, and then a thickness section of the
material layer lying directly beneath the exposed section can be
exposed via the second radiation pattern. The material layer is
then advantageously moved laterally to the optical axis so that a
previously unexposed region of the material layer can be exposed
with the next exposure step.
[0019] In certain embodiments, after generation of the two
radiation patterns, the material layer is moved laterally to the
thickness direction of the material layer (e.g., along the focus
plane of the projection optics), and then once again two radiation
patterns are generated which are focused onto different focus
planes in relation to the material layer. This can allow for the
generation of parallel, two-dimensional sections in the
radiation-sensitive material.
[0020] In some embodiments, the radiation patterns are generated by
a respective illumination distribution generated by the dynamic
mask being projected onto the material layer via projection optics,
and an aberration (e.g., spherical aberration of the projection
optics) can be changed between the projections of the two radiation
patterns. This can be desirable because, when generating the
individual radiation patterns, the electromagnetic radiation
penetrates through material layers of different thicknesses (the
effective thickness of the material layer is different), which can
lead to aberrations, such as dominantly spherical aberrations, when
generating the individual radiation patterns. This effect can be
compensated by dynamic adaptation of aberration (e.g., spherical
aberration). This can be achieved, for example, by changing the
position of moveable lens elements in the projection optics (e.g.,
using piezo-operated z manipulations).
[0021] In certain embodiments, upon generation of the radiation
patterns, an immersion fluid is disposed on the radiation-sensitive
material. The refraction index of the immersion fluid can
correspond to the refraction index of the radiation-sensitive
material. For example, the immersion fluid can fill an intermediate
space between the projection optics and the radiation-sensitive
material. By providing the immersion fluid (the refraction index of
which corresponds to the refraction index of the
radiation-sensitive material), the diffraction-limited projection
may not be effected by the cross-over surface between the immersion
fluid and the radiation-sensitive material.
[0022] In some embodiments, the radiation-sensitive material is in
the form of nonlinear resist, such as 2 photon resist. These types
of resist may not accumulate the exposure dose over a longer
period, but can show a nonlinear reaction to the instantaneous
intensity. It is therefore possible to achieve three-dimensional
structuring in the dynamic scanning operation with high
resolution.
[0023] In certain embodiments, upon generation of the radiation
patterns, a plate of varying thickness made of translucent material
are disposed above the radiation-sensitive material, and an
intermediate space between the radiation-sensitive material and the
plate is filled with an immersion fluid. The plate can compensate
the aforementioned change in aberrations occurring (e.g., spherical
aberrations). The plate can be, for example, a glass plate. With an
effective thickness change of the resist between different
illumination settings (e.g., the z distance between two different
radiation patterns of +10 .mu.m generated in the material layer),
the layer of immersion fluid may advantageously have a thickness
change of +5100 nm and the glass plate a thickness change of -14700
nm. In this case a wavelength .lamda. of 193 nm and a numerical
aperture (NA) of 1.2 is taken as a basis for the radiated
electromagnetic radiation. The refraction index here is 1.7 for the
radiation-sensitive material, 1.43 for the immersion fluid in the
form of water, and 1.56 for the wedge-shaped plate of
SiO.sub.2.
[0024] In some embodiments, the plate is wedge-shaped, and the
respective section of the radiation-sensitive material between the
focus plane of the projection optics and the surface of the
radiation-sensitive material facing towards the plate is also
wedge-shaped in form. The wedge formed by the plate and the wedge
formed in the radiation-sensitive material can have opposing
orientations. With this orientation the aberrations that occur can
be compensated particularly well.
[0025] In certain embodiments, the immersion fluid disposed between
the plate and the radiation-sensitive material also fills a
wedge-shaped volume. The wedge formed by the immersion fluid can
have the same orientation as the wedge formed by the respective
section of the radiation-sensitive material.
[0026] In some embodiments, the surface of the plate facing away
from the immersion fluid and the respective focus plane of the
radiation patterns are parallel to one another.
[0027] In certain embodiments, the latent images generated by the
two radiation patterns in the radiation-sensitive material are
developed at the same time by a single chemical development step.
In certain conventional three-dimensional structuring methods, a
first resist layer is first applied to a wafer, and the layer is
then exposed and a chemical development takes place after the
exposure step, whereupon a further resist layer is applied. It is
possible according to the disclosure to develop the latent images
generated in the individual depth layers of the radiation-sensitive
material at the same time.
[0028] In some embodiments, the layer of the radiation-sensitive
material has a thickness of less than 1 mm. Therefore the thickness
of the layer is at no location on the layer larger than 1 mm.
Optionally, the layer has a thickness of less than 100 .mu.m (e.g.,
less than 20 .mu.m). In certain embodiments, the layer has a
uniform thickness within certain tolerances.
[0029] In some embodiments, the ratio between the thickness of the
layer of the radiation-sensitive material and the area of the layer
is less than 0.01 m.sup.-1 (e.g., less than 0.001 m.sup.-1). The
area refers to the two-dimensional extension of the layer
perpendicular to the thickness direction. In certain embodiments,
the ratio between the thickness of the layer and the area exposed
by the dynamic mask is less than 1 m.sup.-1 (e.g., less than 0.01
m.sup.-1).
[0030] In certain embodiments, the layer of the radiation sensitive
material is arranged on a wafer used in semiconductor
manufacturing, such as a silicon wafer. In some embodiments, the
radiation sensitive material is coated onto the whole surface of
the wafer, which can have a diameter of, for example, 200 mm or 300
mm.
[0031] The features specified with regard to embodiments of the
method listed above can be applied correspondingly to the
apparatus. Embodiments of the apparatus are included in the
disclosure. Advantages listed above with regard to embodiments of
the method also relate to the apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] In the following exemplary embodiments, a method and an
apparatus for structuring a radiation-sensitive material are
described in greater detail via the attached schematic drawings, in
which:
[0033] FIG. 1 shows an apparatus for structuring a
radiation-sensitive material,
[0034] FIG. 2 shows a section of the radiation-sensitive material
structured via the apparatus according to FIG. 1 in two different
positions (I) and (II) during an exposure procedure,
[0035] FIG. 3 shows examples of respective radiation patterns
generated in the two positions (I) and (II) according to FIG. 2 in
the radiation-sensitive material in a top view onto the
radiation-sensitive material layer,
[0036] FIG. 4 shows a perspective view of a material layer
structured via the radiation pattern shown in FIG. 3,
[0037] FIG. 5 shows a section of an apparatus for structuring a
radiation-sensitive material,
[0038] FIG. 6 shows examples of respective radiation patterns
generated in two different positions (I) and (II) in the
radiation-sensitive material in a top view onto the material
layer,
[0039] FIG. 7 shows a sectional view of the radiation-sensitive
material during implementation of a method to illustrate the
extension of the focus plane,
[0040] FIG. 8 illustrates the wavefront aberration in the outlet
pupil when changing the thickness of the radiation-sensitive
material by a certain amount,
[0041] FIG. 9 shows a sectional view of an arrangement of different
layers over the radiation-sensitive material, and
[0042] FIG. 10 shows the wavefront aberration according to FIG. 8
for the arrangement according to FIG. 9.
DETAILED DESCRIPTION
[0043] In the exemplary embodiments described below, elements which
are similar to one another functionally or structurally are
generally provided with the same or similar reference numbers.
Therefore, in order to understand the features of the individual
elements of a specific exemplary embodiment, reference should be
made to the description of other exemplary embodiments or to the
general description.
[0044] FIG. 1 shows an embodiment 10 of an apparatus for
structuring a layer 22 of a radiation-sensitive material. The
radiation-sensitive material layer 22 in the form of a photoresist
or so-called resist used in microlithography is applied to the
surface of a carrier 24 in the form of a wafer by coating. The
wafer can have a diameter of, for example, 200 mm or 300 mm. The
carrier 24 is held by a holding device 27 in the form of a moving
stage or a so-called wafer stage. Furthermore, the apparatus 10 has
a control device 25 for controlling the exposure sequences,
including the dynamic mask 16 and the holding device 27.
[0045] The layer 22 of the radiation-sensitive material has a
thickness d of, for example, 10 .mu.m. The radiation-sensitive
material is configured such that, upon irradiation with a radiation
intensity exceeding a threshold intensity in a specific wavelength
range, a characteristic property of the radiation-sensitive
material is changed. For example, the radiation-sensitive material
22 can be chemically changed in the region exposed above the
threshold radiation intensity such that in a subsequent development
step the radiation-sensitive material 22 can be dissolved away,
whereas the radiation-sensitive material irradiated with a
radiation intensity below the threshold intensity remains
unchanged. The radiation-sensitive material 22 can also be designed
to act conversely so that only the material irradiated with a
radiation intensity above the threshold intensity remains during
the development step, whereas the material which has been
irradiated with a radiation intensity below the threshold intensity
is dissolved out.
[0046] The apparatus 10 includes a light source 12 for generating
electromagnetic radiation. The wavelength of the electromagnetic
beams generated by the light source 12 can be in the visible
wavelength range, but can also be in the UV wavelength range, and
can, for example, have a wavelength of 248 nm or 193 nm. The
electromagnetic radiation 13 generated by the light source 12 is
conveyed by illumination optics 14 disposed in the optical path to
a dynamic mask 16. The dynamic mask 16 is in the form of a
micromirror array, sometimes called a DMD (Digital Micromirror
Device).
[0047] The micromirror array includes a field-shaped arrangement of
10,000.times.10,000 individual micromirrors 18 which respectively
have a mirror surface of 8.times.8 .mu.m. The micromirrors 18 are
mounted on special pivot pins and can be tilted individually. The
inclination of the micromirrors 18 is caused by electrostatic
fields which are generated by switch logics located behind the
micromirrors 18. An individual micromirror 18 forms an optical
switch, and by tilting the micromirror 18 the light beam can be
deflected to such an extent that it no longer falls into the
recording region of downstream projection optics 20, and so is not
imaged into the object plane or focus plane 30 of the projection
optics 20. Each individual micromirror 18 generates one pixel of a
radiation pattern in the focus plane 30. By adjusting the
individual micromirrors 18 the assigned pixels can be switched on
or off.
[0048] The projection optics 20 generally include a plurality of
lens elements. For the sake of simplification only the final lens
element in front of the wafer is shown in FIG. 1. The projection
optics 20 have a high numerical aperture (NA), such as, for
example, 1.2. Disposed between the surface 23 of the
radiation-sensitive material 22 and the final element of the
projection optics 20 is a so-called immersion fluid 28, such as,
for example, water. In some embodiments, the refraction index of
the immersion fluid 28 corresponds to the refraction index of the
radiation-sensitive material 22. Therefore, the position of a
cross-over surface between the immersion fluid 28 and the
radiation-sensitive material 22 may not effect the diffraction
limited projection. The projection optics 20 are designed to image
the illumination pattern generated by the micromirror array with a
reduction of 1:267, and this results in a pixel size of 30 nm with
a field size of 300 .mu.m.times.300 .mu.m in the focus plane
30.
[0049] The carrier 24 in the form of a wafer, and so also the
radiation-sensitive material layer 22 applied to the wafer, is
tilted in relation to the focus plane 30 of the projection optics
20 by a tilt angle of approximately 1.9.degree.. When structuring
the material 22 the carrier 24 is moved along a movement direction
26 tilted by the same tilt angle in relation to the focus plane 30.
The radiation-sensitive material layer 22 is therefore moved in the
plane in which it extends.
[0050] FIG. 2 shows two different positions (I) and (II) of the
radiation-sensitive material layer 22 during the scanning movement
along the movement direction 26. In position (I) shown in the upper
region of FIG. 2 a first radiation pattern 38 is generated in the
material layer 22. The first radiation pattern 38 extends in a
region of the material layer 22 to be structured identified by
reference number 32. The focus plane 30 of the projection optics 20
is located in this region in a lower thickness section of the
material layer 22 and is identified as the first focus plane 30a
with reference to the material layer 22. The extension of the first
radiation pattern 38 in which the radiation intensity exceeds the
threshold intensity of the radiation-sensitive material 22, which
is also called the depth of focus 34, is shown graphically in FIG.
2.
[0051] In the thickness direction of the material layer at the
individual points of the material layer (on lines projected
perpendicularly to the surface 23 of the material layer 22), this
extension or depth of focus 34 is at most 50% of the thickness d of
the material layer 22. However, the depth of focus 34 can also be
smaller by orders of magnitude than the thickness d of the material
layer. The result of the depth of focus 34 thus limited is that the
material layer 22 is only exposed in a limited thickness section
and that in the vertical direction adjacent sections remain
unexposed. During the scanning movement along the movement
direction 26, the radiation pattern changes little by little
depending on pre-specified desired structuring of the region 32 in
the vertical direction.
[0052] As an example, in the lower region of FIG. 2 a position
identified by (II) is shown. In this position the region 32 to be
structured is already pushed further to the right. In order to
further expose the region 32 to be structured, another region in
the image field of the dynamic mask 16 is illuminated. In position
(II) the focus plane 30 of the projection optics 20 is located in a
second focus plane 30b in relation to the material layer 22. In
position (II) a second radiation pattern 40 is generated in the
second focus plane 30b by the dynamic mask 16. The depth of focus
34 of the second radiation pattern 40 is also at most 50% of the
thickness of the material layer 22. Therefore, in position (II) a
thickness section of the region 32 to be structured lying over the
thickness section exposed in position (I) is exposed.
[0053] FIG. 3 shows examples of a first radiation pattern 38 and of
a second radiation pattern 40 in the focus plane 30 (in a top view
as observed in the direction of the optical axis 21 of the
projection optics 20). The radiation patterns 38 and 40 are
examples of radiation patterns generated in the material layer 22
in position (I) and position (II) according to FIG. 2, by which the
three-dimensionally structured material layer 22 shown in FIG. 4
can be produced with individual pyramid-type structures. FIG. 3
respectively shows the field 36 on the material layer 22 which can
be illuminated via the dynamic mask 16. Since in position (II) the
region 32 to be structured is moved to the right in relation to
position (I), the exposed structures of the second radiation
pattern 40 generated in position (II) are moved to the right in
relation to the exposed structures of the first radiation pattern
38 generated in position (I).
[0054] FIG. 7 shows a further extension of the focus plane 30 in
the radiation-sensitive material layer 22 deviating from the
extension shown in FIG. 2 upon exposure by the apparatus according
to FIG. 1. Since the focus plane 30 extends in the x direction
obliquely to the surface 23 of the material layer 22, the effective
thickness 44 through which the electromagnetic radiation 13
penetrates upon generation of the radiation pattern changes. This
type of change to the effective thickness leads to wavefront
aberrations, primarily spherical aberrations. FIG. 8 shows as an
example the distribution of the wavefront aberrations in m.lamda.
in the outlet pupil for a resist thickness change of 769 nm.
[0055] FIG. 5 shows a section of an apparatus 10 for structuring a
radiation-sensitive material 22 that differs from the apparatus 10
according to FIG. 1 only in that the carrier 24 with the
radiation-sensitive material layer 22 is not scanned obliquely to
the focus plane 30 of the projection optics as in FIG. 1. Instead,
the carrier 24 is moved by the holding device in the form of a
movement stage or wafer stage according to the movement pattern 42
shown in FIG. 5.
[0056] FIG. 6 shows as an example a first radiation pattern 138 and
a second radiation pattern 140 for structuring the object shown in
FIG. 4. The structuring method illustrated in FIG. 5 proceeds as
follows. The first radiation pattern 138 is projected into the
radiation-sensitive material 22 in a position of the carrier 24
identified by (I). As with FIG. 1, the depth of focus 34 of the
radiation pattern 138 is limited in the thickness direction of the
material layer 22 to a fraction of the thickness d. After exposure
of the first radiation pattern 138, the material layer 22 is moved
downwards along the optical axis 21 of the projection objective 20
(in the z direction according to FIG. 1). In this position,
identified by (II), a second radiation pattern 140, which is shown
as an example in the right-hand region of FIG. 6, is exposed. The
second radiation pattern 140 is therefore generated in a different
depth layer than the first radiation pattern 138. In some
embodiments, a plurality of radiation patterns are generated along
vertical scans in the direction of the z axis. The carrier 24 is
then moved in the x direction, and a correspondingly formed further
radiation pattern is generated in a region of the material layer
which has not yet been exposed. Here too, the carrier 24 is then
moved vertically and at least one further exposure is
performed.
[0057] In order to compensate the wavefront aberrations
attributable to the varying effective thickness 44, in some
embodiments, the spherical aberration of the projection optics 20
is changed between the projections of the two radiation patterns
138 and 140. For this purpose the projection optics 20 have
moveable lens elements which are moved by piezo-operated z
manipulators.
[0058] FIG. 9 shows an embodiment for compensating the aberrations.
For this purpose a plate 46 made of SiO.sub.2 with a wedge-shaped
cross-section is disposed above the material layer 22, the
intermediate space between the plate 46 and the material layer 22
being filled with immersion fluid 28. The surface 48 of the plate
46 facing away from the immersion fluid 28 and the focus plane 30
are parallel to one another.
[0059] The section of the radiation-sensitive material 22 between
the focus plane 30 and the surface 23 facing towards the plate 46
is wedge-shaped in form. The wedge formed by the plate 46 and the
wedge formed by the section of the radiation-sensitive material 22
have orientations opposite one another. In some embodiments, a
change in the effective thickness 44 of the radiation-sensitive
material 22 is compensated in the x direction by +10,000 nm with a
change in the thickness of the immersion fluid in the z direction
by +5,100 nm and at the same time a change in the thickness of the
plate 46 nm by -14,700 nm. With this compensation, for example, the
wavefront aberration in the outlet pupil illustrated in FIG. 10, is
produced. A wavelength .lamda. of 193 nm and a numerical aperture
(NA) of 1.2 is used as a basis here for the radiated
electromagnetic radiation. The refraction index here is 1.7 for the
radiation-sensitive material 22, 1.43 for the immersion fluid in
the form of water, and 1.56 for the wedge-shaped plate 46 made of
SiO.sub.2.
LIST OF REFERENCE NUMBERS
[0060] 10 apparatus for structuring a radiation-sensitive material
[0061] 12 light source [0062] 13 electromagnetic radiation [0063]
14 illumination optics [0064] 16 dynamic mask [0065] 18 micromirror
[0066] 20 projection optics [0067] 21 optical axis [0068] 22 layer
of radiation-sensitive material [0069] 23 surface [0070] 24 carrier
[0071] 25 control device [0072] 26 movement direction [0073] 27
holding device [0074] 28 immersion fluid [0075] 30 focus plane of
the projection optics [0076] 30a first focus plane in relation to
the material layer [0077] 30b second focus plane in relation to the
material layer [0078] 32 region to be structured [0079] 34 depth of
focus [0080] 36 illuminatable field [0081] 38 first radiation
pattern [0082] 40 second radiation pattern [0083] 42 movement
pattern [0084] 44 effective thickness [0085] 46 plate [0086] 48
surface [0087] 138 first radiation pattern [0088] 140 second
radiation pattern
* * * * *